Wireless local area network (WLAN) technology is developing in three directions.
First, a 60-gigahertz (GHz) band and a 5-GHz band are used in a WLAN in order to enhance a transfer rate. Second, a frequency band of less than 1 GHz is used for a wireless wide area network (WWAN) uses to expand a coverage thereof as compared with conventional WLAN technology. Third, a technique of reducing a link setup time of a WLAN system is adopted.
A WWAN is required to accommodate a remarkably larger number of stations (STAs) than an established WLAN.
Further, WWAN technology may need to support STAs with various service types, such as offloading terminals and sensor terminals, traffic types, and power saving demands.
Therefore, a WWAN system is advancing to reduce collisions in channel access and to achieve efficient power saving by grouping a plurality of STAs.